1. Field of the Invention
The present invention relates generally to an implantable medical device that is associated with telemetry means for wireless data exchange with external unit of the type wherein each of the implantable device each has a calculation processor.
2. Description of the Prior Art
Conventionally the data processing capacity in implantable medical devices has been relatively restricted, primarily due to limitations in the internal memory and processing capacity. However, the amount of processing in the devices has also been kept low in order to economize the energy resources therein. Therefore, raw data generally have been transferred from the implantable device to an external unit for processing whenever a more extensive data analysis has been requested.
U.S. Pat. No. 5,603,331 discloses a data logging system for an implantable cardiac device with a capability of computing and storing histogram arrays of heart rate variability data over a prolonged period of time. A logarithmic data compression algorithm is used to save memory and energy resources in the cardiac device.
U.S. Pat. No. 6,161,043 describes another example of an implantable cardiac device having event recording capability with data compression. A compressed electrogram signal is transmitted from the implantable device to an external programmer according to the following. First, an uncompressed starting value is sent. Nevertheless, following signal samples are sent in the form of delta signals in respect of the starting value. Finally, based on the delta signal, the programmer produces a decompressed signal, which may be presented graphically.
In recent years, however, the processing and data storage capacity of implantable medical devices has increased dramatically. Additionally, battery technology has made many important advancements. Although the external data processing saves energy in the implantable medical device, the process of transferring the source data from the device to the external processing unit also consumes energy. In view of today's comparatively competent processors it is therefore no longer self-evident that external processing is always preferable to internal processing. In fact, transferring the raw data from the implantable medical device may very well demand more energy than performing the calculation in the device and instead transmit the result data for external presentation or further processing.